R. Bonomi R. Kleindienst J. Munilla Lopez M. Chaibi E. Rogez CERN Accelerator School, Erice 2013...
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Transcript of R. Bonomi R. Kleindienst J. Munilla Lopez M. Chaibi E. Rogez CERN Accelerator School, Erice 2013...
R. BonomiR. KleindienstJ. Munilla LopezM. ChaibiE. Rogez
CERN Accelerator School, Erice 2013
CASE STUDY 1: Group 1C
Nb3Sn Quadrupole Magnet
2CERN Accelerator School, Erice 2013
GOAL
• LHC upgrade requires quadrupole magnets with larger apperture.
• Design proposal for Nb3Sn superconducting quadrupole with 150 mm aperture for operation at 1.9 K.
• Study includes coil design, magnetic and mechanical properties.
• The magnetic gradient depends on the width of the coil
• Adding additional coil width leads to diminishing rewards
• A relatively thin design was chosen as a compromise between cost and gradient
-> 2 coils of 10 mm width• Two layers chosen to allow
more possibilities in design for minimizing field errors
0 5 10 15 20 25 30 35 40 45 500
100
200
300
400
500 r=28 mm
r = 50 mm
r = 75 mm
Coil width (mm)
Cen
tral
Gra
dien
t (T
/m) Nb3Sn 1.9 K
3CERN Accelerator School, Erice 2013
COIL WIDTH
N strand 24 Area sc cable 6,032
Strand d (mm) 0,8 Area copper cable 6,032
Cable width (mm) 9,8 Area ins cable 17,675
Cable in thickn. (mm) 1,45 Fill fact 0,341Cable out thickn.
(mm) 1,45 Compression (w) -0,046
Keystone angle 0,00 Compression (t) -0,094Insulation thickness
(mm) 0,15
Cu/Sc ratio 1,00
w
t
4CERN Accelerator School, Erice 2013
CABLE PARAMETERS
•
• Load line plotted for our configuration• Short sample and operational parameters computed• Higher field gradient possible with (118 T/m vs. 83 T/m)• Temperature stability margin higher by ~3K
5CERN Accelerator School, Erice 2013
LOAD LINE
Short Sample
Operational (80%)
Jsc [A/mm2] 2754 2203
Jo [A/mm2] 939 751
I [A] 16611 13300
G [T/m] 147 118
Bpeak [T] 13 10.4
• Coil layout used to compensate higher order multipoles
• Each sector used to cancel out next non-forbidden order
6CERN Accelerator School, Erice 2013
COIL LAYOUT
• Mechanical Design should avoid tensile stress • Thin shell approximation used (26%)• Forces computed using formula:
• Iron yoke supporting 90% of Iss• Collar thickness 20 mm for a maximum stress of 70 MPa• Thickness of shrinking cylinder 12 mm for up to 100 MPa
-> Use of Aluminium possible
7CERN Accelerator School, Erice 2013
MECHANICAL DESIGN
Fx 1.2 MN/m
Fy -2.9 MN/m
σθ 158 MPa
ISSUES
• Both are cuprites, the SC is confined to the CuO plane, mechanism not fully understood
• In both cases high critical current in single crystals, however severly lowered by grain boundries!
• Bi2212, unlike YBCO can be formed to round wires using power in tube process• Compaction and heating have large impact on SC-properties, large parameter space
to optimize
9CERN Accelerator School, Erice 2013
ISSUES: YBCO vs. Bi2212
• The block-coil geometry naturally suppresses extrinsic losses, which typically constitute ~half of all ac losses, which are reduced in the block-coil geometry by the aspect ratio of the cable, typically 10:1
• The simple equivalent block-coil design requires 20% less superconductor than the cosθ design of the same aperture and field strength.
• Furthermore, one of the characteristics of the block-coil model is its scalability. After having studied the basic characteristics of a small aperture block coil magnets, an attempt could be made to design a large aperture magnet in a fast and efficient way by scaling up both the dimension of the aperture and the number of the blocks.
10CERN Accelerator School, Erice 2013
ISSUES: SC COIL DESIGN
• Pre-stress is needed to be sure that no tensile stresses will be applied on the coil• Pre-stress is usually lowered when the magnet is cooled down• Enough amount of pre-stress to remain at compressive state of stresses at every
operation condition is needed.• As a general rule, pre-stress should be as small as needed to accomplish this
condition, plus some safety margin of some Mpa as typical value (0-30 MPa)
11CERN Accelerator School, Erice 2013
ISSUES: ASSEMBLY PROCEDURE